This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Three programs have been developed by the Resource and are used on a daily basis. tcaSIM allows the simulation of complex metabolic networks including the citric acid cycle, glycolysis, gluconeogenesis and anaplerosis. The operator controls all aspects of 13C labeling and fluxes in all pathways. The program generates 13C NMR and HMQC-TOCSY spectra, as well as mass and tandem mass spectra, of numerous metabolites such as amino acids, ketones and glucose. The companion program tcaCALC is used to analyze experimental data, determining the same metabolic parameters as used in tcaSIM from observed NMR or mass spectra. Both these rograms examine the relative flux through pathways, while tcaFLUX determines absolute fluxes from time series of 13C NMR and HMQC-TOCSY spectra. The details of tcaSIM, tcaCALC, and tcaFLUX have been described in previous progress reports.